1. Field of the Invention
The present invention generally relates to a nonvolatile ferroelectric memory device, and more specifically, to a technology of stably controlling a power source applied to a cell capacitor, thereby improving a sensing margin.
2. Description of the Prior Art
Generally, a ferroelectric random access memory (hereinafter, referred to as ‘FeRAM’) has attracted considerable attention as next generation memory device because it has a data processing speed as fast as a Dynamic Random Access Memory DRAM and conserves data even after the power is turned off.
The FeRAM having structures similar to the DRAM includes the capacitors made of a ferroelectric substance, so that it utilizes the characteristic of a high residual polarization of the ferroelectric substance in which data is not deleted even after an electric field is eliminated.
The technical contents on the above FeRAM are disclosed in the Korean Patent Application No. 2002-85533 by the same inventor of the present invention. Therefore, the basic structure and the operation on the FeRAM are not described herein.
Meanwhile, as the pattern size of a semiconductor memory device becomes smaller, an operation voltage of a CMOS device is reduced at the same ratio. When the operation voltage of the CMOS device drops, the power consumption of the semiconductor memory device is also reduced.
In general, a capacitor included in the conventional FeRAM cell corresponds to a device which requires a relatively higher voltage. As a result, when the FeRAM cell is operated, a power voltage VCC is pumped to rise to an external power voltage VEXT level.
However, since the external power voltage VEXT having a high voltage level is also applied to adjacent circuits which do not require the high voltage except a cell capacitor, the power consumption of the semiconductor memory device increases. In addition, the area of the whole system board also increases because an additional power supply circuit for controlling power of the memory cell is included in the outside of a chip.